![]() Moreover, we found that the OE thickness transiently decreased at 5 dpi but recovered fully by 21 dpi, as was the case for the SC numbers (Figs. The data from our study suggest that the SARS-CoV-2 did not infect the brain parenchyma or that the level of infection was below detection limit, although some previous research revealed that SARS-CoV-2 RNA and viral antigen can be detected in the brain 12. 2a), including the olfactory bulb (OB, Fig. Interestingly, no SARS-CoV-2 antigen was detected within the sagittal section of the whole brain (Fig. The numbers of SCs significantly decreased in the VM and VL and could not be determined in the DM due to the complete loss of the OE at 5 dpi, although the damage was recovered almost completely in all regions by 21 dpi (Fig. 1b), which are known to express angiotensin converting enzyme 2 (ACE2), the receptor for SARS-CoV-2 11. ![]() The SARS-CoV-2 antigen was not observed in mature OSNs, as identified by olfactory marker protein (OMP) expression, but in cells around the OSNs, mostly supporting cells (SCs) (Fig. Interestingly, SARS-CoV-2-infected cells were observed not only superficially but also deep within portions of the DM region, including the lamina propria. Using immunofluorescence, we detected a significant number of SARS-CoV-2-positive regions throughout the OE at 2 days post-infection (dpi), but not at 8 dpi (Fig. The hamsters were intranasally inoculated with SARS-CoV-2 at 6-weeks of age and samples were collected at several time points. 1a), to confirm the reproducibility of the OE damage obtained in our previous study 5. Therefore, we first analyzed the local impact of SARS-CoV-2 on the OE tentatively divided into 4 regions: dorsomedial (DM), dorsolateral (DL), ventromedial (VM), and ventrolateral (VL) regions (Fig. Each region has a different vulnerability to external harmful agents dorsomedial side is more vulnerable to methimazole 9, and lateral side is to lipopolysaccharide 10. medial/lateral recess on the medial–lateral axis, zone 1–4 areas on the dorsomedial-ventrolateral axis 8. Olfactory nasal cavity has a complicated structure, divided into multiple regions, e.g. ![]() This study examined the long-term effects of SARS-CoV-2 infection on the CNS using the Syrian golden hamster model, which is a well-established model of COVID-19 that reproduces some features of human disease 7. While the damaged OE is gradually restored 4 and olfactory function is recovered in the animal study 5, many COVID-19 survivors clinically continue to suffer from central nervous system (CNS) symptoms such as depression and memory impairment, as well as chronic olfactory dysfunction in some cases 6. The proposed mechanism underlying this SARS-CoV-2-induced olfactory dysfunction involves severe damage and impairment of the olfactory epithelium (OE) previous data using animal models indicates apoptosis and desquamation of the entire OE, including olfactory sensory neurons (OSNs) 3. Olfactory dysfunction is one of the first and most common symptoms of the coronavirus disease-2019 (COVID-19) 2. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has infected over 215 million people, producing an average lethality of 2.1% worldwide 1. ![]()
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